package com.hello;

public class DFS {
    /**
     * leetcode 200 岛屿数量
     * 给你一个由 '1'（陆地）和 '0'（水）组成的的二维网格，请计算网格中岛屿的数量。
     * 岛屿总是被水包围，并且每座岛屿只能由水平方向和/或竖直方向上相邻的陆地连接形成。
     * 此外，你可以假设该网格的四条边均被水包围。
     *
     * 输入：grid = [
     *   ["1","1","1","1","0"],
     *   ["1","1","0","1","0"],
     *   ["1","1","0","0","0"],
     *   ["0","0","0","0","0"]
     * ]
     * 输出：1
     *
     * 输入：grid = [
     *   ["1","1","0","0","0"],
     *   ["1","1","0","0","0"],
     *   ["0","0","1","0","0"],
     *   ["0","0","0","1","1"]
     * ]
     * 输出：3
     */
    public int numIslands(char[][] grid){
        int count = 0;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                if (grid[i][j] == '1'){
                    dfs(grid,i,j);
                    count++;
                }
            }
        }
        return count;
    }
    private void dfs(char[][] grid, int i, int j){
        if (i < 0 || j < 0 || i >= grid.length || j >= grid[0].length || grid[i][j] == '0') return;
        grid[i][j] = '0';
        dfs(grid,i+1,j);
        dfs(grid,i,j+1);
        dfs(grid,i-1,j);
        dfs(grid,i,j-1);
    }

}
